Congenital malformations, twinning and associated variables in a Brazilian population.

A sample of 6052 newborn children (4968 whites, 1084 Blacks) issued from parents with a generally low socioeconomic level, was studied in relation to congenital anomalies and twinning rates. The observed frequency of major malformations was 1.3% and of minor defects 2.0%. The twinning rate was 1.4%. Race differences were generally nonsignificant in these variables. These results are in agreement with those obtained in some other Brazilian series, but discrepancies were also observed. A total of 13% of the malformations observed proved to be familial, polydactyly being the most common anomaly encountered in this class. The frequency of malformations different from those present in the propositi is higher in their sibships than the general prevalence of defective children found among the sibs of normal babies (13% and 4% respectively). Age, gestation length and exposure of the mothers to noxious agents during pregnancy were not significantly different when the parents of normal and malformed children were compared. On the other hand, as expected, the parents of twins are significantly older than those of single-born, and the gestation length was much reduced in pregnancies resulting in multiple births.